This application claims priority to Japanese Patent Application No. JP2002-008334 filed Han. 17, 2002, which is incorporated herein by reference.
The present invention relates to a semiconductor laser device, and particularly to a high output array type semiconductor laser device including an array of a plurality of semiconductor laser chips.
Recently, semiconductor laser devices have been required to have a higher output performance, and to meet such a requirement, efforts have been made to develop array type semiconductor laser devices each including an array of a plurality of semiconductor laser chips (hereinafter, referred to as xe2x80x9cLD chipsxe2x80x9d).
Such array type semiconductor laser devices have been used in various applications including those associated with medical treatment, optical communication, and the like.
FIG. 3 shows one example of a related art array type semiconductor laser device which includes a plurality of LD chips 21 arrayed on an electrode pattern 13 formed on a sub-mount 12 in such a manner as to be spaced from each other in specific intervals L.
Each of the LD chips 21 has a p-electrode 14 and an n-electrode 15. The LD chips 21 are each activated by injecting a current between both the electrodes 14 and 15, to output laser light from a light emitting point 16 formed in an active layer (not shown) of the LD chip 21.
In this semiconductor laser device, since the LD chips are arrayed in proximity to each other, when the LD chips are individually activated with high outputs, thermal interference may occur among the LD chips due to beat generated by high laser oscillation.
A test for examining thermal interference among LD chips has been performed by example of a semiconductor laser device having the same structure as that shown in FIG. 3.
The semiconductor laser device used in this test is specified such that 11 pieces of LD chips 21 (numbered with LD1 to LD11 in this order from one edge of the semiconductor laser device) are arrayed on the sub-mount 12 in such a manner as to be spaced from each other at equal intervals L, wherein the width of each LD chip is 288 xcexcm and the gap (interval) L between the adjacent LD chips is set to 21 xcexcm.
The result of this test is shown in FIG. 4. In this graph, the abscissa indicates an array position of each LD chip and the ordinate indicates a temperature of the LD chip.
From this graph, it becomes apparent that as the array position of the LD chip becomes closer to the center side of the semiconductor laser device, the number of the LD chips exerting the thermal interference on the LD chip closer to the center side becomes larger, with a result that the temperature of the LD chip closer to the center side becomes higher. Such an LD chip whose temperature has been significantly raised due to thermal interference has a problem that the optical output thereof is reduced and the current is liable to be concentrated thereat, whereby the service life of the LD chip is shortened.
To prevent thermal interference in an array type semiconductor laser device, various methods have been proposed. For example, a method of improving the structure of a heat sink on which LD chips are to be arrayed has been disclosed in Japanese Patent Laid-open No. Hei 6-112596, and a method of controlling the temperature distribution of LD chips by disposing a dummy LD chip causing no laser oscillation among the LD chips has been disclosed in Japanese Patent Laid-open No. Hei 9-83056. In each of these methods, however, it fails to realize a sufficient thermal uniformity over the entire LD chips of the array type semiconductor laser device.
An object of the present invention is to provide an array type semiconductor laser device including an array of LD chips, which is capable of reducing the effect of thermal interference mutually exerted on the LD chips, thereby ensuring a thermal uniformity over the entire LD chips.
To achieve the above object, according to an aspect of the present invention, there is provided a semiconductor laser device including a plurality of semiconductor laser chips each of which has an active layer for forming a light emitting point, said semiconductor laser chips being arrayed on the same substrate in such a manner as to be spaced from each other at intervals, wherein said plurality of semiconductor laser chips are arrayed such that a gap between arbitrary adjacent two laser chips located inwardly from both outermost laser chips positioned at both the edges of said semiconductor laser device is wider than a gap between each of said outermost laser chips and an LD chip adjacent thereto.
With this configuration, the semiconductor laser chips are arrayed such that the gap between arbitrary adjacent two laser chips located inwardly from both the outermost laser chips positioned at both the edges of said semiconductor laser device is wider than a gap between each of the outermost laser chips and an LD chip adjacent thereto. As a result, even if the semiconductor laser device is operated with a high output, each semiconductor laser chip located on the inner side of the semiconductor laser device is less susceptible to the effect of thermal interference exerted from the other semiconductor laser chips. This makes it possible to reduce a deviation in temperature rise among the semiconductor laser chips and ensure a thermal uniformity over the entire semiconductor laser chips, and hence to equalize characteristics of the semiconductor laser chips.
The semiconductor laser device according to the present invention is thus advantageous in suppressing the reduction in optical output of a specific semiconductor laser chip due-to temperature rise, thereby maximizing the optical output of the semiconductor laser device,-and also advantageous in eliminating an inconvenience that the current is concentrated at a specific semiconductor laser chip whose temperature has been raised due to thermal interference, thereby preventing the shortening of the service life of each semiconductor laser chip.